% Schematic of Wavelength Division Multiplexer (Optical Fiber Coupler)
% Author: Jimi Oke
\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}%
\usepackage{textcomp}
\begin{document}
\begin{tikzpicture}[
  box/.style={top color=black!30!blue!5, bottom color=black!30,
  middle color=white},
  media/.style={font={\footnotesize}},
  whitetail/.style={very thick, yellow!8!white},
  bluetail/.style={very thick, blue!90},
  orangetail/.style={very thick, orange!90!black}]

% frame
\fill[gray!50,rounded corners] (-5,-2) rectangle (7.5,2);

% coupler box
\draw[thick, rounded corners] (0,-.3) rectangle (2.5,.3);
\filldraw[rounded corners, box] (0,-.3) rectangle (2.5,.3);

% fiber leads
\draw[bluetail] (-4,1) to[out=-30,in=180] (0,.08);
\draw[whitetail] (-4,-1) to[out=30,in=180] (0,-.08);

\draw[very thick, gray] (0,.08) -- (2.5, .08);
\draw[very thick, gray] (0,-.08) -- (2.5, -.08);

\draw[orangetail] (2.5,.08) to[out=0,in=210] (6.5,1);
\draw[whitetail] (2.5,-.08) to[out=0,in=150] (6.5,-1);

% labels
\path[media,fill=white,draw=black] (-4.4,-1.2) node {O2}
             (-4.4, 1.2) node {O1}
             ( 6.9,-1.2) node {I2}
             ( 6.9, 1.2) node {I1};

\node[media,right] at (2,-3)   {I1: In from gain medium};
\node[media,right] at (2,-3.5) {I2: Out to wattmeter for monitoring};
\node[media,right] at (-5,-3) {O1: Connects to Faraday isolator};
\node[media,right] at(-5,-3.5) {O2: Nd:YAG pump input (1.06 \textmu m)};
\end{tikzpicture}
\end{document} 

